Record carrier having a main file system area and a virtual file system area

ABSTRACT

The present invention relates to a recordable record carrier having a user area (UA) for storing user data and a management area (MA) for storing management data. The invention further relates to a recording apparatus for recording information on such a record carrier and a corresponding recording method. In some applications it is useful to translate the main file system into an alternative virtual file system. To reduce the mount times and power consumption needed for reconstruction of the virtual file system, it is proposed that the management area (MA) comprises a main file system area ( 70 ) for storing main file system data (mFS), a virtual file system area ( 71 ) for storing virtual file system data (vFS) in a raw format, and an indicator area ( 72 ) for storing an indicator (ID) indicating whether the main system data (mFS) and the virtual file system data (vFS) are mutually consistent. Only if the indicator (ID) indicates an inconsistency does the virtual file system data (vFS) need to be reconstructed from the main file system data (mFS) when the virtual file system data (vFS) is required by an application. Otherwise, the virtual file system data (vFS) can be directly retrieved from the record carrier without reconstruction.

The present invention relates to a recordable record carrier having auser area for storing user data and a management area for storingmanagement data. The invention further relates to a recording apparatusfor recording information on such a recordable record carrier and acorresponding recording method. The invention further relates to acomputer program for implementing said methods. In particular, thepresent invention relates to an optical record carrier such as a smallform factor optical (SFFO) disc.

In some applications it is useful to translate the file system used on arecordable record carrier into another file system that can be exposedacross a standard interface to a host that does not understand theoriginal file system, which will be called main file system in thefollowing, but that does understand the other file system, which will becalled virtual file system in the following. An example is the mountingof a rewritable SFFO disc which uses a universal disc format (UDF) filesystem in a CompactFlash II (CFII) form factor drive that exposes a fileallocation table (FAT) file system to the host. In the following,recordable shall mean that information can be stored on the recordcarrier once or several times, i.e. rewritable record carriers shall becovered by this term as well.

Typically, some structures or parts of the exposed file system will bestatic, for instance those containing volume descriptions and basicparameters, and some other structures or parts will be volatile, forinstance those detailing directories and the allocation of files. Thestatic parts of the exposed virtual file system can be cached to therecord carrier without problems. They may be put, for instance, in adedicated file in the management data area However, caching the volatilepart of the exposed virtual file system on the record carrier is notstraightforward. Many hosts and applications will not be aware of thefact that there are instances in which (part of) the address space isexposed from the drive to the outside world using an alternative(virtual) file system. In addition, it is also very often not desiredthat the hosts and applications are aware of this, because otherwiseusers and software developers could take it for granted and the hostwould be expected to act accordingly, i.e. maintain all associatedstructures. If one of the hosts or applications updates the main filesystem on the record carrier, the cached virtual file system, inparticular its volatile parts, will be inconsistent with the main filesystem on the record carrier.

Reconstructing the directory structure for the virtual file system,without further measures, is always a time and power consuming task. Itis therefore an object of the present invention to provide a recordablerecord carrier, a recording apparatus for recording information thereon,and a corresponding recording method wherein the required time,processing and record carrier access as well as power consumption can bedramatically reduced.

This object is achieved according to the present invention by arecordable record carrier as claimed in claim 1, whose management areacomprises

-   -   a main file system area for storing main file system data of a        main file system,    -   a virtual file system area for storing virtual file system data        of a virtual file system in raw format, and    -   an indicator area for storing an indicator indicating whether        the main system data and the virtual file system data are        consistent.

This object is further achieved by a recording apparatus as claimed inclaim 8, comprising

-   -   recording means for recording main file system data of a main        file system in a main file system area of said management area,        virtual file system data of a virtual file system in raw format        in a virtual file system area of said management area, and an        indicator indicating whether the main file system data and the        virtual file system data are consistent in an indicator area of        said management area,    -   reading means for reading said user data and said management        data,    -   memory means for storing said virtual file system data,    -   conversion means for converting said main file system data into        said virtual file system data and vice versa for storage on the        record carrier and/or for output to an external host device if        said indicator indicates an inconsistency between the main file        system data and the virtual file system data, and    -   an interface for communicating with a host device.

A recording method for recording information on a record carrier onwhich originally only main file system data are stored is defined inclaim 11 and comprises the steps of:

-   -   reading main file system data of a main file system stored in a        main file system area of said management area,    -   converting said main file system data into said virtual file        system data for storage on the record carrier and/or for output        to an external host device,    -   storing said virtual file system data in a virtual file system        area of said management area in raw format,    -   storing an indicator indicating whether the main system data and        the virtual file system data are consistent in an indicator area        of said management area.

A recording method for recording information on a record carrier onwhich main file system data as well as virtual file system data arestored is claimed in claim 12 and comprises the steps of:

-   -   reading an indicator, which indicates whether main file system        data of a main file system stored in a main file system area of        said management area and virtual file system data of a virtual        file system stored in raw format in a virtual file system area        are consistent, from an indicator area of said management area,    -   reading said main file system data from said main file system        area and reconstructing at least part of said virtual file        system data from said main file system data if said indicator        indicates a inconsistency,    -   reading at least part of said virtual file system data from said        virtual file system area, and    -   exposing the virtual file system data to an external host        device.

The present invention is based on the idea to define and store anindicator on the record carrier indicating whether main system data andvirtual file system data, which are both stored on the record carrier inparticular areas, are consistent or not. If the virtual file system ismounted and the main file system was updated since the last time thestructures of the virtual file system were cached, the virtual filesystem needs to be reconstructed from the main file system stored on therecord carrier. If however, the virtual file system is mounted and themain file system was not updated since the last time the structures ofthe virtual file system were cached, the virtual file system iscompletely retrieved from the record carrier. This prevents the need toreconstruct the virtual file system from the main file system,dramatically reducing time, processing and record carrier accessrequired, and thus reduces the power consumption.

According to the invention, the virtual file system data are stored onthe record carrier in a raw format. This means that the virtual filesystem data are stored in an optimized way to reduce the required memoryspace. Compared with the main file system data stored in the normalformat on the record carrier, less memory space is needed since, forinstance, much of the padding is removed.

The user area and the management area are not necessarily contiguous,they may be interleaved, and/or part of the management data area, e.g.the virtual file system area, may be a file in the main file systemarea, or the space occupied by the virtual file system data may beremoved from the address space presented to the main file system.

According to a preferred embodiment, the static and volatile parts ofthe virtual file system data are stored in separate entities on therecord carrier, in particular in a static area and a volatile area ofthe virtual file system area This further reduces the required time andpower consumption if the indicator indicates an inconsistency betweenthe main file system data and the virtual file system data In this case,only the volatile parts have to be reconstructed from the main filesystem data stored on the disc while the static parts of the virtualfile system data can be retrieved from the record carrier but need notbe reconstructed from the main file system data, which would haverequired an additional time and power consumption. If there is noinconsistency, both the static and the volatile parts of the virtualfile system data are retrieved from the record carrier, and noreconstruction from main file system data is required.

Tracking whether the main file system data has been updated can beimplemented by several measures. According to a preferred embodiment,the indicator comprises the last update date of the main file systemdata and of the virtual file system data Comparing the dates will revealwhether the cached virtual file system data, or at least the cachedvolatile parts thereof, are still valid or whether there is aninconsistency. According to an alternative embodiment, as claimed inclaim 4, a flag is set at the time of updating and caching of thevirtual file system data, which flag indicates that the virtual filesystem data are valid. This flag is updated or reset when the main filesystem data are updated independently, but not the virtual file systemdata, thus indicating that the virtual file system data are invalid andthat there is a high risk of an inconsistency.

Preferably, the indicator area is present in a location on the recordcarrier that is easily accessible to the drive. Such locations include,for instance, a disc navigation (DN) area, the logical volume integritydescriptor (LVID), or a chip in the record carrier, for instance a chipin disc. For instance, the last update date of the main file system datamay be retrieved from the time stamp of the LVID, and the indicator maybe stored in the ImplementationUse field in the ImplementationUse areaof the LVID. The LVID is a structure specific to UDF. The LVID willautomatically be updated even by a non-aware UDF implementation.

According to another preferred embodiment, the virtual file system areafurther comprises a directory area for storing the directory structureof the virtual file system. Since reconstructing the directory structurecan be a time and power consuming task, this considerably reduces thetime involved in retrieving and using the virtual file system data Thisdirectory information in this form is not part of the originalspecification of the virtual file system, neither is the directoryinformation written using the main file system present on the recordcarrier in this format optimized for use with the virtual file system.The location of these data may need to be faked by mapping it on top ofthe main file system structures which are not accessed directly by thevirtual file system. This measure is also of benefit if the virtual filesystem data are isolated from the main file system data, i.e. if thevirtual file system data are located in a dedicated image. The virtualfile system data may be in a file in the user area described by the mainfile system. Foreign file systems, e.g. the virtual file system, may beembedded in a file of another file system, e.g. of the main file system.This file is usually called an image.

The present invention is preferably applied to an SFFO disc whichpreferably uses a UDF file system as its main file system and a FAT filesystem as its virtual file system. When applying the invention, all dataneeded for browsing the SFFO disc without actually accessing files iscached, thus dramatically improving mount times and the power requiredto mount the virtual file system, especially if the UDF was not updatedor is not relevant, in the case of a dedicated virtual file systemimage. In this latter case the files in the virtual file system area arenot specified separately in UDF. In addition, the proposed inventionenables the exposure of the virtual file system in an optimal waywithout putting any burden on the main file system.

The invention will now be explained in more detail with reference to thedrawings, in which

FIG. 1 shows a block diagram of a recording apparatus according to thepresent invention,

FIG. 2 shows a flow chart of a first embodiment of the recording methodaccording to the present invention,

FIG. 3 shows a flow chart of another embodiment of a recording methodaccording to the present invention,

FIG. 4 shows a disc and memory layout and the steps of the recordingmethod according to the present invention, and

FIG. 5 shows the disc layout and the steps of another embodiment of therecording method.

FIG. 1 shows a recording apparatus 1 according to the present inventionto which two host devices 2 and 3 are connected. The recording apparatus1 comprises interfaces 4 and 5 for communication with said host devices2, 3. Furthermore, the recording apparatus 1 comprises recording andreading means 6 for recording information on a recording medium 7 andfor reading information from said medium 7, e.g. an optical disc. Saidmedium 7 has a user area UA for storing user data and a management areaMA for storing management data. It generally uses a main file systemmFS, e.g. a UDF file system, which is stored in a main file system area70. Via the interface 5, e.g. an ATAPI interface, host devices 3 capableof interpreting the main file system mFS can communicate with therecording apparatus 1 and use the recording medium 7.

For legacy host devices, however, such as host device 2, which cannotinterpret the main file system, an additional virtual file system vFS isrequired for communication between the host device 2 and the recordingapparatus 1 via the interface 4, which is, for instance, a CFIIinterface. Such virtual file system data vFS are stored in memory means8 in the recording apparatus 1. A conversion unit 9 is provided in therecording apparatus 1 for conversion of the main file system data mFSstored on the record carrier 7 into the virtual file system data vFSstored or to be stored in the memory unit 8 or vice verse Thus, thevirtual file system data vFS, for instance FAT file system data, can beexposed across the interface 4 to the host device 2.

At least a portion of the virtual file system data vFS is also stored onthe record carrier 7 in a particular virtual file system area 71. Thisis generally not the virtual file system itself but information derivedfrom it or virtual file system data in a raw format. Such raw data donot enable the host device 2 to use the virtual file system foraccessing the record carrier 7, but are provided on the record carrierto optimize the conversion process from the main file system to thevirtual file system. Furthermore, the stored part of the virtual filesystem generally does not cover all of the files on the record carrierat all times as the main file system does. A distinction is preferablymade between volatile and non-volatile data of the virtual file systemdata vFS.

Still further, an indicator ID is additionally stored on the recordcarrier 7 in a particular indicator area 72. This indicator ID is usedto indicate whether the main file system data mFS and the virtual filesystem data vFS are consistent or not.

The function of the recording apparatus 1 and the recording methodaccording to the present invention will now be explained in more detail.FIG. 2 shows a flow chart of a first embodiment of a recording method.In a first step S10, main file system data mFS which are alreadyprovided on the record carrier are read therefrom. Such main file systemdata mFS are then converted in step S11 into virtual file system datavFS if the record carrier 7 is mounted for the first time in therecording apparatus 1. Such virtual file system data vFS are stored inthe subsequent step S112 in memory 8 as well as, at least partly, on therecord carrier 7 in a virtual file system area 71. Finally, in step S13,the indicator D indicating in this case consistency between the mainfile system and the virtual file system is stored in the indicator area72.

Another embodiment of the recording method according to the presentinvention, which takes into account that virtual and main file systemdata are already stored on the record carrier, is shown in the flowchart of FIG. 3. In a first step S20, the indicator ID is read from therecord carrier and evaluated in step S21. If the indicator ID indicatesthat the main file system data mFS and the virtual file system data vFSare mutually consistent, the virtual file system data vFS are completelyread from the record carrier (S22) and outputted (S23) so that a hostdevice using the virtual file system can access the record carrier.

If the indicator ID indicates an inconsistency in step S21, at leastpart of the main file system data mFS is read (S24) from the recordcarrier and subsequently converted (S25) into virtual file system datavFS which are finally again outputted (S23). Thus, the virtual filesystem needs to be reconstructed from the main file system only in thosecases in which there is an inconsistency, which dramatically reducestime and power consumption in such cases.

FIG. 4 shows the disc layout and the memory layout and illustrates thesteps of another embodiment of a recording method according to thepresent invention. In the first line, the layout of the logical volumeof an optical rewritable disc 7 is shown. It comprises a lead-in areaLIA including the lead-in LI and disc navigation data DN, a lead-outarea LOA including the lead-out LO and a program area PA including userdata, main file system volume structures such as a UDF volume, and mainfile system file entries such as UDF file entries UDF FE.

The main file system data consist of volume descriptors in a contiguousspace at the beginning of the program area PA and file descriptors thatcan be scattered throughout the remaining program area PA, for instanceinterleaved with actual user data, i.e. files, or preferably in acontiguous area, which is preferably located at the end of the programarea in the case of SFFO.

The user area UA and management area MA, described above and shown inFIG. 1, are not necessarily contiguous, they may be interleaved, and/orthe virtual file system data area, which is part of the management dataarea, may be a file in the main file system data area, or the spaceoccupied by the virtual file system data area may be removed from theaddress space presented to the main file system.

If the disc 7 is mounted for the first time in a FAT enabled CFII drive,the UDF, i.e. the main file system data, will be read and translated(S30) in the drive (referred to above as the recording apparatus 1) toFAT. The static parts are mainly derived from the UDF volume structures,the volatile parts are mainly derived from the UDF file entries. Theobtained FAT, in particular its static part, volatile part, anddirectory structure, is stored in the memory 8 and can be exposed acrossthe CFII interface 4.

Upon an unmount command of the disc the constructed FAT is translated(S31) back into the UDF and written to the disc 7. An additionalindicator is stored on the disc 7, for instance in an easily accessiblelocation, such as an indicator area ID in the disc navigation area DN,indicating whether the cached FAT is valid or not. Alternatively or inaddition, the last update date for the FAT and of the UDF may berecorded on the disc 7, e.g. in the disc navigation area DN so that acomparison of these dates will reveal whether the cached FAT is stillvalid. Still further, said indicator may be implemented using thelogical volume integrity descriptor LVID, for instance by retrieving thelast update date of UDF from the time stamp in the LVID and/or byincluding a flag that indicates that the cached FAT is valid in theImplementationUse field in the ImplementationUse area of the LVID.

If the UDF is supposed to cover files added during the FAT operation,the UDF on the disc 7 also needs to be updated which can, however, bedelayed until the next dismount or until the next mount under UDF. Ifthe UDF has not been changed before the next mount of FAT, it can beignored and only the FAT memory structures stored on the disc 7 areloaded into the memory 8 as shown in the last two lines of FIG. 4.

If the UDF has been changed before the next mount of FAT, only thestatic part of the FAT is retrieved from the disc 7 directly, e.g. froma static area within the disc navigation area DN and/or the UDF volume,whereas the volatile part of the FAT is reconstructed from the UDF onthe disc 7 as shown in FIG. 5. The FAT starts at the beginning of thestorage space. The generated FAT image is then mapped over the UDFvolume space as shown in FIG. 5, last line.

The drive checks the inconsistency flag. If this not raised, the drivereads the cached vFS directly into memory. If it is raised, the drivemounts the mFS, reads at least the static part of the vFS, andreconstructs the new situation for the vFS. Then the data area isexposed with FAT virtually mapped, as shown in FIG. 5, to the beginningof the address space. Physical block number 0, i.e. the beginning of theUA, is logical block number 0 within FAT. The data area of the FAT filesystem starts at the beginning of the UDF partition (logical blocknumber 0 for UDF), which usually directly follows the area with the UDFvolume structures. It should be noted that it is possible to change UDFwithout making it inconsistent with FAT, e.g. by changing an extendedattribute, which is not a concept known to FAT.

The indicator may be recorded in different locations such as the discnavigation area, e.g. in a separate structure such as an indicator area,with the static parts of the virtual file system (FAT), in a chip indisc or in MRAM (magnetic random access memory) in the drive.Furthermore, the directory structure of the virtual file system may alsobe recorded on the disc to save time and power consumption duringreconstruction of the virtual file system.

A particular implementation of the invention will now be explained. Theinvention may be applied on an SFFO disc which is mounted in a CFII formfactor drive in a digital camera. In memory the UDF is translated intoFAT, generating static FAT structures, e.g. the boot record, which arewritten to disc, and further generating the FAT tables and arepresentation of the directory structure. The drive exposes a FAT basedCFII interface to the digital camera Still images are transferred fromthe camera to the SFFO disc. The FAT structures are updated in memory.Dirty flags indicating that the contents of the structures the dirtyflags are related to are not verified or guaranteed to be consistent,are set for each added file and FAT as a whole.

If the batteries of the camera run out before the drive is ejected, noproblem arises for the SFFO drive since an NVRAM, preferably MRAM, isused as the memory. As soon as the camera has new batteries, the drivewill perform a consistency check. Upon dismounting of the drive, thevolatile parts of FAT, in particular FAT tables and FSInfo structure,are written to disc as well as the directory information. The FATallocation is translated into UDF structures for the new and updatedfiles. The UDF on SFFO is updated. Part of the latter update writes theLVID. It is written in the ImplementationUse field of theImplementationUse area of the LVID that the cached FAT is valid.

Next time the FAT is mounted it will check the LVID for the CachedValidindicator. If this is present, both the static and volatile parts of FATare retrieved from disc, as well as the directory information. If it isnot present, it means that some UDF implementation has written the LVIDmost recently and that the FAT and directory structures need to bereconstructed from the UDF on disc. Thus the present inventiondrastically reduces the mount times and energy required for mounting thevirtual file system.

1. Recordable record carrier having a user area (UA) for storing userdata and a management area (MA) for storing management data, saidmanagement area comprising a main file system area (70) for storing mainfile system data (mFS) of a main file system, a virtual file system area(71) for storing virtual file system data (vFS) of a virtual file systemin raw format, and an indicator area (72) for storing an indicator (ID)indicating whether the main system data (mFS) and the virtual filesystem data (vFS) are consistent.
 2. Record carrier as claimed in claim1, wherein said virtual file system area (71) comprises a static areafor storing static parts of said virtual file system data and a volatilearea for storing volatile parts of said virtual file system data (vFS)so that, if the indicator (ID) indicates an inconsistency between themain file system data (mFS) and the virtual file system data (vFS), onlythe volatile parts of the virtual file system data (vFS) need to bereconstructed from the main file system data (mFS).
 3. Record carrier asclaimed in claim 1, wherein said indicator (ID) comprises the lastupdate date of the main file system data (mFS) and of the virtual filesystem data (vFS).
 4. Record carrier as claimed in claim 1, wherein saidindicator (ID) comprises a flag which is set when the virtual filesystem data (vFS) are updated, indicating that the virtual file systemdata (vFS) are valid, and which is reset when the main file system data(mFS) are updated independently, indicating that the virtual file systemdata (vFS) are invalid.
 5. Record carrier as claimed in claim 1, whereinsaid indicator area (72) is present in an easily accessible location, inparticular in a disk navigation area (DN), in a logical volume integritydescriptor (LVID), or in a chip in the record carrier (7).
 6. Recordcarrier as claimed in claim 1, wherein said virtual file system area(71) further comprises a directory area for storing the directorystructure of the virtual file system.
 7. Record carrier as claimed inclaim 1, wherein said main file system is a Universal Disc Format (UDF)file system, and wherein said virtual file system is a File AllocationTable (FAT) file system.
 8. Recording apparatus for recordinginformation on a recordable record carrier (7) having a user area (UA)for storing user data and a management area (MA) for storing managementdata, said apparatus comprising recording means (6) for recording mainfile system data (mFS) of a main file system in a main file system area(70) of said management area (MA), virtual file system data (vFS) of avirtual file system in raw format in a virtual file system area (71) ofsaid management area (MA), and an indicator (ID) indicating whether themain file system data (mFS) and the virtual file system data (vFS) areconsistent in an indicator area (72) of said management area (MA),reading means (6) for reading said user data and said management data,memory means (8) for storing said virtual file system data (vFS),conversion means (9) for converting said main file system data (mFS)into said virtual file system data (vFS) and vice versa for storage onthe record carrier (7) and/or for output to an external host device (2,3) if said indicator (ID) indicates an inconsistency between the mainfile system data (mFS) and the virtual file system data (vFS), and aninterface (4, 5) for communicating with a host device (2, 3). 9.Recording apparatus as claimed in claim 8, wherein said recording means(6) and said reading means (6) are adapted for accessing an optical disk(7), in particular a small form factor optical disk using a universaldisc format, and wherein said interface (4) is adapted for communicatingwith a compact flash form factor drive (2) using a file allocation tablesystem.
 10. Recording apparatus as claimed in claim 8, wherein saidmemory means (8) comprise a MRAM unit.
 11. Recording method forrecording information on a recordable record carrier (7) having a userarea (UA) for storing user data and a management area (MA) for storingmanagement data, said method comprising the steps of reading main filesystem data (mFS) of a main file system stored in a main file systemarea (70) of said management area (MA), converting said main file systemdata (mFS) into said virtual file system data (vFS) for storage on therecord carrier (7) and/or for output to an external host device (2, 3),storing said virtual file system data (vFS) in a virtual file systemarea (71) of said management area (MA) in raw format, storing anindicator (ID) indicating whether the main system data (mFS) and thevirtual file system (8) data (vFS) are consistent in an indicator area(72) of said management area (MA).
 12. Recording method for recordinginformation on a recordable record carrier (7) having a user area (UA)for storing user data and a management area (MA) for storing managementdata, said method comprising the steps of reading an indicator (ID),which indicates whether main file system data (mFS) of a main filesystem stored in a main file system area (70) of said management area(MA) and virtual file system data (vFS) of a virtual file system storedin raw format in a virtual file system area (71) are consistent, from anindicator area (72) of said management area (MA), reading said main filesystem data (mFS) from said main file system area (70) andreconstructing at least part of said virtual file system data (vFS) fromsaid main file system data (mFS) if said indicator (ID) indicates aninconsistency, reading at least part of said virtual file system data(vFS) from said virtual file system area (71), and exposing the virtualfile system data (vFS) to an external host device (2).
 13. Recordingmethod as claimed in claim 12, further comprising the steps of settingthe indicator (ID) such that it indicates an inconsistency if thevirtual file system data (vFS) and/or the main file system data (mFS)are changed, and storing the set indicator (ID) in said indicator area(72).
 14. Computer program comprising computer program means for causinga computer to perform the steps of the method as claimed in claim 11when said computer program is run on a computer.